Field of the Invention
The invention relates in general to a wireless signal receiving system, and more particularly to a technology for eliminating a channel effect in a wireless signal receiving system.
Description of the Related Art
Digital television broadcasting has matured and become popular with the ever-improving communication technologies. In addition to being transmitted through cables, digital television signals may be propagated in form of wireless signals via base stations or artificial satellites. Wireless signals are inevitably affected and interfered by transmission environments during the transmission process. Thus, a receiver ends needs to evaluate corresponding channel effects to eliminate the influence the channel effects have on signal contents through equalization in order to correctly decode received data.
Digital terrestrial multimedia broadcasting (DTMB) is a main digital television broadcasting standard currently adopted in the Mainland China. According to the DTMB specification, signals in a multi-carrier mode are formed by a series of alternating data headers and frame bodies. From a time-domain perspective, the data headers may be regarded as periodically placed between multiple frame bodies. Contents in the header frames are known, and may thus serve as reference data for channel estimation at a DTMB receiver end. FIG. 1(A) shows a functional block diagram of a stereotypic channel effect eliminating device 100. A receiver 100 includes a time-domain channel estimating circuit 11, a fast Fourier transform (FFT) circuit 12 and an equalization circuit 13. The time-domain channel estimating circuit 11 generates a channel estimation result h according to reference data r (e.g., a data header). The FFT circuit 12 converts the channel estimation result h and a data signal y (e.g., a frame body) respectively to a frequency-domain channel estimation result H and frequency-domain data Y. The equalization circuit 13 then generates an equalized signal X according to the frequency-domain channel estimation result H and the frequency-domain data Y to reconstruct the contents of the data signal y. However, in the event where the known data (the reference signal r) has an inadequate length, the channel estimation result h the time-domain channel estimating circuit 11 generates according to the reference data r cannot reflect the true channel effect, such that the channel effect eliminating device 100 may fail to correctly reconstruct the contents of the data signal y.
In view of the above, an improved channel effect eliminating device 120, as shown in FIG. 1(B), has become available. One difference between the channel effect eliminating device 120 and the channel effect eliminating device 100 is that, the channel effect eliminating device 120 further includes a decision circuit 14 and an inverse fast Fourier transform (IFFT) circuit 15. The equalized signal X is transmitted to the decision circuit 14, which applies hard decision on the equalized signal X to generate a decision processed signal Z. The IFFT circuit 15 then converts the hard decision processed signal Z to a feedback signal z, which serves as a part of the reference data for channel estimation of the time-domain channel estimating circuit 11. Compared to the channel effect eliminating device 100, including the feedback signal z in the reference data is equivalently increasing the length of known data. Therefore, the channel estimation result h the time-domain channel estimating circuit 11 generates according to the reference signal r and the feedback signal z better reflects the true channel effect, hence allowing the channel effect eliminating device 120 to more correctly reconstruct the contents of the data signal y.